The present invention relates to an indicator for displaying information such as a period of time, through the change of a color tone, and the like.
A period-indicating element is known, which utilizes a phenomenon that, when a liquid is applied onto a frosted glass plate or a water-writing paper sheet, the glass plate or paper sheet exhibits a different color from that prior to the application of the liquid (see JP-B-63-13545). However, the liquid is retained only on the surface of the glass plate or paper sheet according to the prior art element, and thus the evaporation of the liquid or migration of the liquid to other material starts while the time period-indicating element is being transported, or it is stored in a sealed state prior to use. Accordingly, the amount of the retained liquid decreases prior to the time use of the period-indicating element, so that the element is discolored during the storage, or the displayed period varies. In addition, since the amount of the retained liquid is small, the effects of an insecticide or an aromatic may not be sufficiently exhibited, when it is used as a liquid.
An object of the present invention is to provide an indicator which has good storage properties and suffers from less variation in displaying a time period during use.
The present invention relates to an indicator comprising a porous resin material, and a liquid retained in the pores of said porous resin material, which satisfies the following relationships:
W1xe2x89xa780 and
(W1xe2x88x92W2)xe2x89xa720
wherein W1 is a whiteness of the porous resin material, and W2 is a whiteness of the indicator.
The indicator herein used means an element which indicates, for example, a period of time, and can be used in various fields as explained below.